Missiles are typically attached to an aircraft by a pair of hooks that must withstand large forces based on the weight of the missile and the motion of the aircraft. While the aircraft flies, takes-off, or lands, the aircraft may expose the missile to multiple g-forces, which can multiply the amount of stress experienced by the hooks to maintain the attachment of the missile to the aircraft.
To withstand the large amount of stress, the hooks are typically fixed to the missile. Thus when the missile is launched from the aircraft the hooks often remain protruding outward from an outer skin of the missile.
Some missiles have utilized linearly retractable hooks instead of hooks fixed to the missile. The linearly retractable hooks require a large amount of space and weight within the missile to withstand the large amount of stress endured by the hooks while the aircraft operates.